[CQ-Contest] receiver evaluations

[al_lorona at agilent.com]

Hi, Eric,

The test you described is called the Noise Power Ratio (NPR) test, and it is used more and more to simulate the multi-carrier conditions that an amplifier is likely to see. It is primarily for transmit and receive amplifiers working at high frequency, but I don't know if it has ever been applied to the entire receiver, RF-to-AF. 

You need a very good signal generator to create that kind of a signal. The noise has to be wideband and perfectly flat, with sharp corners. The notch is very difficult to create. You want to get a notch about one channel bandwidth wide, which in a typical ham receiver would be about 2.5 kHz for SSB or 500 Hz for CW. An analog filter can be used, but it is far from ideal. Nowadays, an RF generator with arbitrary digital modulation is used and the NPR modulating signal usually has to be downloaded from a computer into the generator. The signal is usually in I-Q; that is, there are two channels which are combined to give you the necessary amplitude-and-phase-versus-time waveforms that describe the spectrum required. You can see a glimpse of what I'm talking about at:

http://eesof.tm.agilent.com/docs/adsdoc15/examples/tutorial/NoisePowerRatio.html

Regards,

Al  W6LX



-----Original Message-----
From: Eric Scace K3NA [mailto:eric at k3na.org] 
Sent: Tuesday, March 18, 2003 1:06 PM
To: Cq-Contest
Subject: [CQ-Contest] receiver evaluations


   For some time now, ARRL and others have included in their collection of receiver performance test the blocking dynamic range and
two-tone 3rd-order IMD, using two signals with some spacing such as 5 or 20 kHz.  Of course, two strong signals doesn't emulate much
of the real world.

   I recall a variation of this test that was used by AT&T to evaluate performance of multi-channel radio receivers used to carry
large quantities of telephone channels.  Naturally, one did not want a strong signal in one telephone channel to contaminate the
signals being carried in other channels on the route.  The test was performed as follows:
   -- instead of two signals being applied to the receiver under test, a broadband noise was applied.  The noise was modified by
notching out the bandwidth for one channel; i.e., essentially no noise in the notched channel.
   -- measurements were made in the channel corresponding to the notch.
   -- noise power to the receiver was increased until the point at which the measured channel started to exhibit degradation (e.g.,
increase in the noise floor).

   This seems to be a more general test that corresponds more closely to what a contest receiver experiences on a crowded band;
i.e., LOTS of signals attacking the receiver across the band.

   Could those who are knowledgeable about receiver evaluation methodology comment as to whether such a test would be more likely to
accurately characterize the ability of a receiver to hold up against strong signals outside of the operating passband than the
two-signal test method?

   Thanks.

-- Eric K3NA


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